Lung function tests

Lung Function tests are performed in our Lung Function Unit by a friendly team of respiratory physiologists. The tests are used to assess how well your child’s lungs are working and can be used to track lung growth and development overtime. Our unit offers a number of different tests, each of which will measure a different functional purpose of the lungs. We aim to make the tests fun and engaging for the children and young people attending.

This webpage from Great Ormond Street Hospital (GOSH) describes what will happen when your child attends for a lung function test.

Below is a list of tests performed in the Lung Function Unit. More details on each test will be found below or if you click on the test you will be directed to its webpage for more information.

Your child will either have one or a number of these tests depending on what your doctor has requested. These could take place on the same day as your child’s outpatient appointment, in the lung function lab or on the ward if they are currently an inpatient.

Do I need to bring anything?

You should receive a letter in the post or via MyGosh with the instructions on where to come for the test. No other preparation is needed for the test.

The person bringing your child for the test should have ‘Parental Responsibility’ for them. Parental Responsibility refers to the individual who has legal rights, responsibilities, duties, power and authority to make decisions for a child. If the person bringing your child does not have Parental Responsibility, we may have to cancel the test.

Lung function tests

The lung function laboratory has a number of machines designed to test different aspects of your child’s lung function. We will explain each machine as we need to use them. Here is a bit more information about each of the tests we offer.


This is the most common lung function test we perform. This looks at how fast your child can blow air out of their lungs through the airways. Your child will be asked to breathe in until they are full, and then blow out as hard and as long as they can through a mouthpiece.

There are a range of computer-based incentives such as blowing out candles to encourage your child to do this as well as they can.

Bronchodilator response (BDR)

Sometimes after spirometry, your child may need a BDR test to work out the effect of a medication (salbutamol) on the airways. Your child will do spirometry before taking the medication and then again 15 minutes afterwards to see if there is any change in their lung function.

The physiologist will help your child understand how to take the medication using an inhaler.

Fractional exhaled nitric oxide (FENO)

This test can measure inflammation in the airways. Your child will need to take a deep breath through a device similar to a straw. They will then have to blow out gently and smoothly as if they are cooling a cup of tea.

We use games to encourage your child to blow out correctly for this test.

Gas transfer (TLCO)

This test looks at how well oxygen moves into the lungs from the air we breathe and how well it passes from the lungs into our blood. Your child will need to take a big breath to fill their lungs completely with a harmless gas mixture and then hold their breath for 10 seconds before blowing out all the air until they are empty.

Lung volumes (plethysmography)

For this test your child will sit inside a box a bit like a telephone box. They will do a range of breathing exercises to calculate the volume of air in the lungs.

Are there any risks?

All of the tests will be performed by a respiratory physiologist. Each test your child needs to perform will be explained beforehand and you will have a chance to ask any questions or raise any concerns you may have.

How long will the test last?

Testing can last between 15 to 90 minutes, depending on the number of different tests that are required. Your appointment letter will give you a rough idea of how long testing will take.

The tests require co operation so we will give your child clear instructions and plenty of encouragement to help them to achieve reliable results. We try to maintain your child’s interest throughout testing by making the experience as enjoyable as possible and allowing time to rest between tests.

Getting the results

The results for your test will be uploaded onto our electronic patient record system for your doctor to view. If you are seeing your doctor in clinic or later that day, they will go through the results of this test. If you are not seeing the doctor on the same day they will still be able to view the results ready for your next appointment. They will contact you if there is anything that your child needs to do before their next appointment.

Compiled by:
the Lung Function Unit in collaboration with the Child and Family Information Group
Last review date:
November 2022